1. Field of the Invention
The present invention relates to a method of manufacturing a circuit board such as a printed circuit board, and more particularly, to a circuit board embedding a thin film capacitor in which the thin film capacitor is fabricated using a laser lift-off process.
2. Description of the Related Art
With a trend of smaller size, lighter weight, higher speed and higher frequency in electronic devices, the electronic devices are increasingly required to be highly integrated. To this end, vigorous studies have been conducted on technologies for integrating passive and active devices into a board to enhance efficiency.
In related efforts to achieve smaller electronic devices, studies have been under way to embed many passive devices such as a resistor, a capacitor and an inductor in the PCB in place of mounting them thereon. A capacitor accounts for about 60% of the passive devices, which is a considerable proportion, thus heightening interests in an embedded capacitor. As described above, the capacitor, when embedded in the PCB in place of being mounted thereon, allows the electronic devices to be reduced in size by about 40% and enhances electrical characteristics at a high frequency due to low impedance (<10 pH) at the high frequency.
Such an embedded capacitor generally includes two copper foils (conductive layers) and a prepreg insulating layer therebetween. As an example, U.S. Pat. No. 5,261,153 discloses a technology of manufacturing a capacitor-embedded printed circuit board by depositing uncured dielectric sheets between conductive foils. Also, U.S. Pat. No. 6,541,137 discloses a capacitor embedding a high temperature thin film using a dielectric material, in which a barrier layer is formed to prevent a conductive layer from oxidizing due to heat treatment at a high temperature of 400 to 800° C.
As described above, a dielectric film of the thin film capacitor needs to be heat treated at a high temperature to be crystallized to have a high permittivity.
However, in the conventional capacitor embedded in the PCB, the insulating layer is formed of polymer and thus not capable of undergoing high temperature heat treatment which causes the board to be deformed.
Moreover, when the dielectric layer is deposited on the copper foil and heat treated, the copper foil may be easily oxidized. Here, the capacitor may be significantly degraded in desired characteristics due to effects of an oxidized interface.
These problems have led to an intense demand for developing a process in which an embedded capacitor with a dielectric film requiring high temperature heat treatment is beneficially applied to a multilayer circuit board such as the PCB.